The correct answer is A) Firing of a red star signal. The firing of a red star signal is used by a rescue unit to indicate "Avast hauling" or cease hauling operations. This is the standard distress signal prescribed by the International Code of Signals, which is the reference for all maritime signaling and communication. The other options are incorrect because: B) a green star signal does not have a specific meaning related to cease hauling, C) three white star rockets are used for general distress signaling, and D) an orange smoke signal is used to indicate the location of a person in the water, not to signal the rescue unit.